A53C-0901 1340h
Observation of nocturnal NO3 and N2O5 in the urban atmosphere by laser-induced fluorescence technique
Nitrate radical (NO$_{3}$) and dinitrogen pentoxide (N$_{2}$O$_{5}$) play critical roles in the nocturnal atmosphere. NO$_{3}$ and N$_{2}$O$_{5}$ are important as intermediates in the NOx loss process. NO$_{3}$ can react with various hydrocarbons and contribute the lifetimes of them. N$_{2}$O$_{5}$ can be removed from the atmosphere on the aerosol surface. To discuss lifetime of NOx in the atmosphere, it is essential to know the nighttime chemistry of NO$_{3}$ and N$_{2}$O$_{5}$ accurately. However, there are few studies on the observation of NO$_{3}$ and N$_{2}$O$_{5}$ previously. In this study, a sensitive analyzer for measuring NO$_{3}$ and N$_{2}$O$_{5}$ has been developed utilizing the thermal conversion and laser-induced fluorescence (LIF) technique. The calibration of the analyzer has been carried out by the series of N$_{2}$O$_{5}$ decomposition and gas phase titration of NO$_{3}$ by NO. As a result of characterization and optimization of the instrument, the sensitivity of the NO$_{3}$ detector was 0.21 cps ppbv$^{-1}$ mW$^{-1}$ and the limit of detection reached 4 and 6 pptv for NO$_{3}$ and N$_{2}$O$_{5}$, respectively, for {\it S/N} = 1 and 10-min averaging. The analyzer has sufficient potential to detect nighttime NO$_{3}$ and N$_{2}$O$_{5}$ in the atmosphere. Then, to discuss NOx loss, a field observation of NO$_{3}$ and N$_{2}$O$_{5}$ were conducted during winter and spring at an urban site. In the urban atmosphere, NO$_{3}$ level was quite low due to significant abundance of NO. However, 100 - 800 pptv of N$_{2}$O$_{5}$ was observed. The steady-state analysis for NO$_{3}$ and N$_{2}$O$_{5}$ was conducted to know the loss rate of NOx via NO$_{3}$ and N$_{2}$O$_{5}$. Consequently, the loss rates of NO$_{3}$ and N$_{2}$O$_{5}$ were estimated as 1.0 x 10$^{-2}$ and 5.2 x 10$^{-4}$ s$^{-1}$, respectively. Nocturnal loss of NOx was determined as 5.6 ppbv night$^{-1}$, as significant as the daytime loss of NOx via NO$_{2}$ + OH. N$_{2}$O$_{5}$ is important as NOx sink when the ambient temperature is low enough for N$_{2}$O$_{5}$ to survive for a long time. To discuss NOx budget, it is important to know how much NOx can survive and be supplied out of the source area.
A53C-0902 1340h
Kinetics Studies of the Atmospheric Oxidation of Alkynes
The reaction of peroxy radicals (RO2) - produced in the atmospheric oxidation of hydrocarbons - with nitric oxide (NO) is a key reaction in the formation of ground level ozone in urban environments. Experimental measurements using the Turbulent Flow Chemical Ionization Mass Spectrometric (TF-CIMS) kinetics technique and thermodynamic and kinetic parameters recovered from the MG2MS computational approach are presented in order to elucidate the atmospheric oxidation pathway of 2-butyne. The results that indicate that the atmospheric oxidation of 2-butyne (and probably all alkynes) does not directly lead to peroxy radicals, and thus may have a dramatically lower ability to produce ozone than other hydrocarbon classes.
A53C-0903 1340h
Absorption Cross Sections of Formaldehyde in the Ultraviolet Spectral Region of 28100-28500 cm$^{-1}$ (351-356 nm) at 0.04 cm$^{-1}$ (0.0005 nm) Resolution: Implications for {\it in Situ} Laser-Induced Fluorescence Detection
Formaldehyde (HCHO) is the principal intermediate in the oxidation of hydrocarbons in the troposphere. Because HCHO has a diurnally-averaged lifetime in the upper troposphere (UT) of about 8-12 hours, it can serve as a tracer for recent convection and a proxy for volatile organic compounds (VOCs) emitted. Model studies have shown that convectively injected acetone [(CH$_{3}$)$_{2}$CO], hydrogen peroxide (H$_{2}$O$_{2}$), and methyl hydroperoxide (CH$_{3}$OOH) can be significant sources of HOx in the UT, producing HCHO as an intermediate. Thus, a measurement of HCHO is important for the understanding of HOx chemistry and ozone production, especially in the tropical transition layer (TTL). The absence of fast, precise, and accurate measurements of acetone and peroxides make {\it in situ} HCHO measurements even more important. Simultaneous measurement of HCHO along with OH, HO$_{2}$, and other species involved with ozone and HOx chemistry will provide insight into the question of convection's impact on ozone production in the TTL and the stratospheric budget of convectively transported organic pollutants. Accurate absolute absorption cross sections of HCHO are not only needed in satellite-based remote sensing experiments using differential optical absorption spectroscopy but also in laser-induced fluorescence (LIF) HCHO flight platforms for {\it in situ} measurements. LIF provides a high sensitivity technique that takes advantage of the high absorption cross sections of the narrow single rotational lines of HCHO. However, previous measurements of the absorption spectrum of HCHO in the UV region have never been rotationally resolved. In this study, we obtained rotationally resolved absolute cross sections of HCHO in the spectral region of 28100-28500 cm$^{-1}$ (351-356 nm) at 0.04 cm$^{-1}$ (0.0005 nm at 353.5 nm) resolution using Fourier transform spectroscopy. HCHO concentration was determined by condensed-phase iodometric titration, and gaseous HCHO generation was performed using a novel micro-injector technology. Spectra were acquired with high wavenumber accuracy, and the pressure and temperature dependences of the cross sections were also studied. High-resolution spectra are useful as they can be readily degraded to confirm low-resolution measurements, and our resulting HCHO absorption spectra were compared to existing literature at lower resolutions.
A53C-0904 1340h
Chemistry and Photochemistry of NO$_{y}$ in Thin Water Films Using a Newly Designed Apparatus
A 102-L borosilicate glass reaction cell has been equipped to measure both gas phase chemistry as well as the chemistry in thin surface films simultaneously. Two spectroscopic methods are combined in this unique apparatus. Gases are measured with long path Fourier transform infrared spectroscopy (FTIR), while an attenuated total reflectance (ATR) FTIR probe can measure the changes in the composition of thin water films. This system has been applied to the heterogeneous hydrolysis of nitrogen dioxide as well as the photolysis of surface nitric acid, which has been proposed to be a source of HONO. Results from these studies and their atmospheric implications will be discussed.
A53C-0905 1340h
Selective Characterization of Benzo[a]pyrene Diones Using LC/MS/MS
Benzo[a]pyrene (B[a]P) is a known carcinogenic pollutant emitted into the atmosphere as a result of incomplete combustion. Its major photolysis products are B[a]P-1,6-dione, B[a]P-3,6-dione, and B[a]P-6,12-dione. The diones are functionalized polycyclic aromatic hydrocarbons (PAHs) with substituent oxygen atoms attached to them. The Environmental Protection Agency (EPA) has also categorized the compounds as possible carcinogens. Furthermore, the inherent polarity of the compounds make them mobile throughout the environment. Previous studies show standards of B[a]P and B[a]P-3,6-dione, B[a]P-1,6-dione and B[a]P-6,12-dione being successfully separated using high performance liquid chromatography coupled to atmospheric pressure chemical ionization (LC/APCI-MS), with mass-to-charge ratios (m/z) of 252 and 283, respectively. This paper will discuss further advances in the characterization of B[a]P diones achieved by employing LC/APCI-MS/MS technique. This further confirms the presence of B[a]P diones by yielding a unique daughter fragment with m/z of 255, which corresponds to the loss of a C=O group from the parent dione. The experiments have been confirmed by utilizing theoretical molecular modeling with Spartan (Wavefunction, Inc.). The implication of these results on the field of tropospheric photochemistry will be discussed.
A53C-0906 1340h
Observations and Preliminary Interpretation of Hydrogen Peroxide (H$_{2}$O$_{2}$) and Peroxyacetic Acid (PAA) in the Atmosphere During INTEX-NA, Summer 2004.
Observations of hydrogen peroxide (H$_{2}$O$_{2}$) and peroxyacetic acid (CH$_{3}$C(O)OOH, PAA) in the troposphere will be reported with an emphasis on PAA. Measurements were made by the Caltech chemical ionization mass spectrometer (CIMS) and by the University of Rhode Island HPLC-Fluorescence instrument. Both were flown on the NASA DC-8 aircraft during the Intercontinental Chemical Transport Experiment - North America (INTEX-NA) science campaign (summer 2004). PAA, heretofore unquantified in the troposphere, was observed in significant concentrations throughout the middle and upper troposphere during INTEX-NA. The primary production mechanism for PAA is the addition of the perhydroxyl (HO$_{2}$) radical to the peracetyl (CH$_{3}$C(O)OO) radical. This mechanism is in direct competition with NO$_{2}$ addition to peracetyl which produces PAN. Peracetyl radical is formed initially through the oxidation of hydrocarbons and can be regenerated through the decomposition of PAN. The presence of PAA may indicate one of two situations: 1) relatively low NO$_{x}$ to high hydrocarbon photochemical environment, or 2) relatively low NO$_{x}$ to high PAN photochemical environment. The loss mechanisms for PAA in the troposphere are not fully understood. Photolysis rates measured in the lab give PAA a lifetime on the order of 3-4 weeks for mid-latitude summertime conditions (Orlando, et. al., 2003). The lifetime of PAA with respect to oxidation by OH has not been measured, but is estimated to be on the order of 1 week, based on measured OH reaction rates with similar species. Unlike PAN, PAA is not expected to decompose at warm temperatures. Wet and dry deposition rates are not known for PAA. The Henry's law coefficient has been determined, K$_{H}$ = 840 M/atm at 298 K (O'Sullivan, et. al, 1996), and shows depositional loss to be of minor importance. The observations will be compared to values inferred from theoretical production/loss mechanisms.
A53C-0907 1340h
Novel Instrumentation for In-Situ Carbon Monoxide Measurements in the Troposphere and Stratosphere
The carbon monoxide mixing ratio has been significantly altered by the burning of fossil fuels and can serve as an indicator of pollution transport, with vertical profiles of CO showing considerable structure related to regional pollution sources. These profiles are measured in-situ by airborne instrumentation that is capable of accurately determining the CO mixing ratio in a rapid fashion. Currently, this mixing ratio is determined by using lead-salt diode lasers to perform tunable diode laser absorption spectrometry (TDLAS), resulting in an instrument that requires frequent user intervention to realign the optical cell and adjust the laser. The recent emphasis on using Unmanned Aerial Vehicles (UAVs) to make atmospheric measurements has created a need for more robust, autonomous analytical instrumentation. We will present a carbon monoxide analyzer based on combining emerging quantum cascade laser (QCL) technology with Off-Axis Integrated Output Spectroscopy (Off-Axis ICOS). The spectroscopic technique will be described in detail along with in-situ data from multiple NASA DC-8 flights demonstrating the instrument's capability to autonomously measure CO to better than 200 ppt in less than one second, without the need for any user intervention. Ongoing efforts to extend the instrument's capabilities to measure multiple species (CO, N$_{2}$O, and CH$_{4}$) while making it suitable for UAV deployment will also be discussed.
A53C-0908 1340h
Behavior of the Hydroxyl and Hydroperoxy Radicals in a Smog Chamber Study
The hydroxyl radical (OH) and the hydroperoxyl radical (HO$_{2}$), together called HO$_{x}$, are significant reactants in the production of pollutants such as ozone and fine particles in real and simulated environments. The concentrations of OH and HO$_{2}$ and the OH reactivity were measured as part of a smog chamber study to assess the sensitivity of ozone on volatile organic compounds (VOC) and nitrogen oxides (NO$_{x}$). The experiments were carried out in the EPA next-generation smog chamber at University of California, Riverside, CA in September and October 2003. A matrix of chamber experiments were performed at graduated levels of VOC and NO$_{x}$ designed of replicate the range of VOC and NO$_{x}$ concentrations typically found in urban and rural environments. The OH and HO$_{2}$ radicals were measured by laser-induced fluorescence (LIF) in addition to the standard chamber measurements of O$_{3}$, VOCs, NO, NO$_{2}$, HNO$_{3}$, HCHO and H$_{2}$O$_{2}$. Box models with four different photochemical mechanisms were used to calculate the simulated concentrations of OH, HO$_{2}$ and other species for each chamber experiment. The model simulations were compared with the measurements in the smog chamber. While OH and HO$_{2}$ generally show the expected behavior, three interesting observations emerge. First, modeled HO$_{2}$ concentrations were generally lower than the observations, which was consistent with the underestimation of observed H$_{2}$O$_{2}$ and O$_{3}$. Second, OH budget analysis show that additional OH sources are required to balance the observed OH sinks. Third, simultaneous observations of dark OH and HO$_{2}$ after the light was turned off suggest the presence of unidentified dark HO$_{x}$ sources. The evidence supporting these observations will be discussed.
A53C-0909 1340h
Environmental Chamber Studies of Mercury Reactions in the Atmosphere
Mercury is released into the environment through both natural and anthropogenic pathways. The cycling and fate of mercury in atmospheric, soil, and water ecosystems is impacted by various factors, including chemical transformation and transport. An understanding of these processes is critical for predicting the impact of mercury emission controls and future mercury concentrations. The chemical transformations of elemental mercury in the atmosphere were studied to determine the role of atmospheric chemistry in the mercury cycle. The rates of the gas phase reactions of elemental mercury with molecular bromine, chlorine, and fluorine, the atomic halogens, BrO, ClO, ozone, and the nitrate radical were studied at room temperature in a 17.3 m$^{3}$ environmental chamber. The fate of elemental mercury resulting from these chemical reactions was addressed by measurement of reactive gaseous mercury, particle-phase mercury, and reactive mercury lost to the chamber surfaces during the experiments. The implications of these chemical reactions and others studied in environmental chambers for the cycling of elemental atmospheric mercury will be discussed. This work has been funded wholly or in part by the United States Environmental Protection Agency Office of Research and Development. It has been subjected to peer review and approved for publication.
A53C-0910 1340h
Measurements of NO$_{2}$ in Ambient Air Using a Solid-State Photolytic Converter
Measurement of trace levels of nitrogen dioxide (NO$_{2}$) remains an important issue for increasing our understanding of tropospheric ozone production and the distribution of precursor species. A fast-response, highly specific photolytic converter for NO$_{2}$ using a light-emitting diode (LED) light source has been developed and characterized in both laboratory experiments and measurements in ambient air. An overview of the technology will be presented, highlighting the important features of the photolytic converter and its use with chemiluminescence detectors (nitric oxide [NO] + ozone [O$_{3}$]). Performance tests conducted both in the laboratory and the field will be presented. Results from ambient measurements of NO$_{2}$ in conjunction with other reactive nitrogen species and ozone from an aircraft platform will be presented to demonstrate the converter performance and to explore the chemical relationships observed.
A53C-0911 1340h
Measurement of the Henry's Law Coefficient and the Solvolysis Rate of PAN in n-Octanol
Peroxyacetic Nitric Anhydride (PAN) is one of the most abundant odd-nitrogen species in the atmosphere in part because of it's low solubility in water. Much less is known about the solubility of PAN in non-polar media that are characteristic of some plant materials or aerosol particles. n-Octanol is often used as a surrogate for non-polar media in the determination of the environmental fate of pollutants. The solubility of PAN in n-octanol was measured over a temperature range of 273 to 298K, using a bubble column flow system with GC/ECD detection. The observed Henry's Law coefficients ranged from 26 to 90 M/atm and the first order solvolysis rate constants were quite low, less than 5 x10$^{-5}$ sec$^{-1}$. The implications of these findings for the heterogeneous transport and loss of PAN will be discussed.
A53C-0912 1340h
First deployment of a newly developed PIT-MS instrument for VOC measurements: Results from the ITCT-NEAQS 2004 experiment and comparison with GC-MS
Volatile organic compounds (VOCs) were measured during the Intercontinental Transport and Chemical Transformation - New England Air Quality Study (ITCT-NEAQS 2004) in July-August 2004 with a newly developed PIT-MS (Proton Transfer Ion Trap - Mass Spectrometry) instrument for the first time during a field experiment. The instrument is based on the principle of PTR-MS (proton-transfer-reaction mass spectrometry): VOCs are ionized using proton transfer reactions and detected with a mass spectrometer. As opposed to a quadrupole mass filter in PTR-MS, the PIT-MS instrument uses an ion trap mass spectrometer, which has the following advantages. First, an ion trap has extended analytical capabilities of identifying VOCs by performing collision-induced dissociation (CID) and ion molecule reactions. Second, the ion trap has a nearly 100% duty cycle for a full mass spectrum, whereas a quadrupole transmits only ions of one mass at a time. Here, the results obtained in the marine boundary layer downwind of New York, Boston, and forested areas by PIT-MS are compared with GC-MS (gas chromatography/mass spectrometry) measurements of many hydrocarbons, including oxygenated, and with GC-ECD (gas chromatography/electron capture detection) measurements of peroxyacetyl nitrates (PANs). The PIT-MS instrument described had, during the experiment, a detection limit of <300 pptv for 1-min measurements for all measured VOCs. Furthermore we explore how the analytical capabilities of the PIT-MS instrument can be used to identify VOCs that are indistinguishable by PTR-MS.
A53C-0913 1340h
Development of a Single Photon Laser Induced Fluorescence Technique for the Detection of Atmospheric NO
The NO$_{x}$ family (NO$_{2}$ and NO) plays a pivotal role in the photochemistry of the atmosphere. NO$_{x}$ affects the concentration of the OH radical in the troposphere. It is also an important component of production of ozone in the troposphere. Having a clear idea of the spatial and temporal distribution of NO$_{x}$ is therefore important in obtaining a clear picture of the processes that contribute to the overall photochemistry of the atmosphere. Laser-induced fluorescence (LIF) is one of the methods of direct measurement of NO and NO$_{2}$ concentrations. A new method using a kHz pulse repetition frequency YAG pumped Ti:Sapphire laser using single photon excitation of NO at 226 nm wavelength is described and demonstrated. The NO fluorescence is observed at 247 nm wavelength. This is part of a multispecies detection system designed to measure a suite of species important to atmospheric composition and photochemistry in a compact package suitable for airborne and other field measurements.
A53C-0914 1340h
Overtone-Induced Decarboxylation: A Potential Sink for Atmospheric Di-acids
Atmospheric photochemistry induced by solar excitation of vibrational overtone transitions has recently been demonstrated to be of importance in cleaving weak bonds (in HO2NO2) and inducing intramolecular rearrangement followed by reaction (in H2SO4). Here we propose another potentially important atmospheric process: the decarboxylation of organic diacids. To demonstrate this possibility, we have calculated (using the GAUSSIAN 98 quantum chemistry package) the decarboxylation pathways for malonic acid and its mono-hydrate and performed preliminary photolysis experiments. The barrier to the gas-phase decarboxylation was calculated to be in the range 26-28 kcal/mol at the B3LYP/6-311++G(3df,3pd) level of theory, in good agreement with previous results, suggesting that excitation of vOH ≥3 of either one of the OH stretching modes is sufficient to supply the energy needed for the decarboxylation. A low energy isomer of the malonic acid-water complex forms an 8-membered, multiply hydrogen bonded structure; decarboxylation of such complexes has a barrier of 20-22 kcal/mol, suggesting that complexes excited to vOH ≥ 2 possess sufficient energy to react. Photolysis of aqueous solutions of malonic acid was carried out using a filtered Xe lamp (to eliminate IR and UV light). A 3- to 4-fold increase in acetic acid production was observed in irradiated vs. non-irradiated solutions. We suggest that the overtone-induced decarboxylation of malonic acid and its water complex is competitive with wet deposition of the acid and with gas phase reaction with OH for removal of the acid.
A53C-0915 1340h
An Aircraft Instrument for Simultaneous, In-situ Measurement of NO3 and N2O5 via Cavity Ring-down Spectroscopy
This paper describes a cavity ring-down spectrometer (CaRDS) specifically designed and constructed for installation on the NOAA WP-3 aircraft for in situ measurement of NO3 and N2O5 as part of the ICARTT 2004 campaign. While similar to our previous previously described CaRDS instrument (Brown et al, 2002), significant improvements were implemented to improve the signal-to-noise ratio, the time resolution, and the inlet transmission efficiency of the measurement system. Moreover, drastic reductions in overall size and weight were achieved to meet the requirements for installation on the aircraft. An inlet suitable for use with an aircraft was installed. This paper describes the specifics of these design changes and the resultant improvements in the measurement. Also presented are sample flight data taken with the new instrument. Additionally, this paper briefly describes a sealed automated filter changer that was designed and constructed to remove particulate matter in the airflow while having minimal loss of NO3 and N2O5. This filter changer, along with other improvements, allowed autonomous operation during the lengthy aircraft flights.
A53C-0916 1340h
Preliminary Evidence for Ozone Production Within Yosemite Valley
Ozone concentrations within the Yosemite National Park have violated the California human health standard for over a decade. Elevated ozone concentrations have historically been attributed to poor regional air quality and to the long-range transport of ozone and ozone precursors into the park from outside sources. However, there has been increasing concern that local, within Yosemite, pollutant emissions may contribute to Yosemite's air quality issues. During peak tourist season, half a million people visit the Park every month with most people arriving in cars to visit a geographically small feature of the Park, Yosemite Valley. Thus, during peak season on average 6000 cars and 63 buses visit Yosemite Valley daily and campfires burn nightly in up to 472 Valley campsites. In part to address concern over local emission sources, the National Park Service installed several air quality sampling stations within and surrounding Yosemite Valley over the last 4 years. We use the 2000 to 2003 ozone, nitrogen oxide, and meteorological measurements to investigate if local ozone production occurs as air masses are advected over Yosemite Valley pollution sources, predominately located in the eastern Valley. Due to measurement limitations, the amount of ozone produced is difficult to quantify, but on a typical summer day is likely to be at least 5ppb and possibly greater than 20ppb over a 4km transect. This analysis suggests that the air quality in the eastern end of the Yosemite Valley may be worse than previously known and we recommend that more detailed air quality measurements be made in this area. This work was produced at the University of California, Lawrence Livermore National Laboratory (UC LLNL) under contract W-7405-ENG-48 (Contract 48) between the U.S. Department of Energy (DOE) and The Regents of the University of California (University) for the operation of UC LLNL. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, products or process disclosed, or represents that its use would not infringe privately-owned rights. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. (UCRL-ABS-206474)
A53C-0917 1340h
Atmospheric Determination of NO, NO$_{2}$, NO$_{y}$, and PAN in Rural Canadian Environments Using an Automated Measurement System
As part of the Canadian Air and Precipitation Monitoring Network (CAPMoN) measurements of NO, NO$_{2}$, NO$_{y}$, and Peroxyacetic nitric anhydride (PAN) were made to characterize the ambient concentrations of different nitrogen compounds in order to estimate their contributions to the total nitrogen dry deposition flux at regional-scale sites in Canada. Fully automated systems, complete with calibration routines and remote data acquisition have been operating at two rural locations since August 2002. These measurement sites are located in Kejimkujik National Park, Nova Scotia and at the Centre for Atmospheric Research Experiments (CARE) located in Egbert, Ontario (approx. 80 km north of Toronto). Continuous measurements of NO, NO$_{2}$, and NO$_{y}$ were made using a Thermo Environmental Instruments trace level chemiluminescence-based analyzer with the conversion of NO$_{2}$ and NO$_{y}$ to NO by photolysis and molybdenum converters respectively. PAN measurements were made every five minutes by direct injection into a designed gas chromatograph equipped with a pulse discharge detector (GC-PDD) and calibrated several times daily using photochemically generated PAN standards. Detection limits for all these measurements were found to be on the order of 50 parts per trillion (ppt). Details of the measurement system, the challenges of validating low level measurements, and preliminary findings related to the similarities and differences found at these sites will be discussed.
A53C-0918 1340h
Deployment of a Cryo-less GC System at Appledore Island for VOC Measurements during the ICARTT 2004 Campaign
A large suite of nonmethane hydrocarbons (NMHCs), halocarbons, alkyl nitrates and oxygenated volatile organic compounds (OVOCs) were measured at Appledore Island as part of the ICARTT 2004 campaign using a prototype, cryo-less concentrator system coupled to a gas chromatograph (GC) equipped with two flame ionization detectors (FIDs), one electron capture detector (ECD), and a mass spectrometer (MS). The trace gas system utilizes novel cooling technologies for the concentration of air samples without the use of liquid nitrogen or solid absorbents, making this system unique and robust. A 1500 cc sample was trapped at -175 C with a custom Kleemenko cooler (MMR Technologies, Inc.) coupled to an all Silonite coated (Entech Instruments, Inc.) stainless-steel valving system that was built in-house for sample concentration. After samples were concentrated, they were isolated, rapidly heated and injected. After injection, the sample was quantatively split in to 4 sub-streams, each feeding a separate column-detector pair. A Shimadzu GC-17A housed the 4 different separation columns which were coupled to the FIDs, ECD and the Shimadzu QP-5050A MS. The NMHCs were primarily separated on two different separation columns (PLOT and VF-5ms) equipped with FIDs. The halocarbons and alkynitrates were measured using an OV-1701 column coupled to the ECD. Selected hydrocarbons, halocarbons, and OVOCs were separated and quantified using an OV-624 coupled to the MS. To demonstrate the capabilities of this novel, cryo-less trace gas analytical system, results from this GC system are compared with measurements conducted concurrently during the ICARTT campaign at Appledore Island using a PTR-MS and from canister samples analyzed in our laboratory at UNH using a GC-FID/ECD/MS system. Overall, very good agreement between all three measurement techniques were observed for most compounds measured during the ICARTT study period.
A53C-0919 1340h
Halocarbon Distributions at Appledore Island, ME and Thompson Farm, Durham, NH during ICARTT 2004
Halocarbons were measured during the ICARTT 2004 campaign at two AIRMAP monitoring sites, Appledore Island, 6 miles off the coast of NH and Thompson Farm, 10 miles inland in Durham, NH. An automated GC system using electron capture detectors (ECDs) was used at Thompson Farm for measurement of halocarbons every 40 minutes. The Thompson Farm GC system is a dual stage trapping system using liquid nitrogen. The measurement precision for each of the halocarbons ranged from 0.3-15 percent. Hourly canister samples were collected at Appledore Island from July 1 through August 13, 2004 for halocarbons. Canister samples were collected in 2-liter electropolished stainless steel canisters (UCI) and pressurized to 40 psig using a single head metal bellows pump. Canister samples were returned to the laboratory for analysis by gas chromatography using ECD in conjunction with mass spectrometry. Approximately 1032 samples were analyzed during the course of the campaign. Throughout the sampling period Appledore Island was largely influenced by marine air masses on a regular basis. The mixing ratios of bromoform, dibrmomethane and methyl iodide often track each other indicating that these gases have similar marine sources. There is a large variability of these gases on an hourly time scale in the marine environment, as compared to the anthropogenically produced halocarbon, C$_2$Cl$_4$. Overall, ratios of bromoform and dibromomethane were similar at both Appledore Island and Thompson Farm, except for the period from July 14-15. Back trajectory analysis of the air mass sampled during this period indicates that this air mass originated from out over the North Atlantic, was transported to the northwest then south along the coast of Maine and then out over Appledore Island. The increased mixing ratios of dibromomethane without a concurrent increase in bromoform could indicate that a coastal source of dibromomethane was encountered during the transport of this clean marine air mass. Coastal sources of halocarbons are not well understood and further analysis of the full suite of halocarbons measured during this study will provide much insight to coastal zone influences on atmospheric halocarbon concentrations.
A53C-0920 1340h
PTR-MS Measurements of Atmospheric VOCs during the ICARTT 2004 Campaign
Two proton transfer reaction mass spectrometers (PTR-MS, Ionicon Analytik) were employed for atmospheric measurements of volatile organic compounds (VOCs) during the ICARTT 2004 summer campaign. One PTR-MS was located at UNH's Thompson Farm Observing Station (latitude 43.11, longitude -70.95) and a higher sensitivity instrument (PTR-MS-hs) was located at Appledore Island (latitude 42.99, longitude -69.34). Both instruments were run under the same conditions with a drift tube pressure of 2 mbar with an electric field of 600 V and a 20 second dwell time for measuring 23 VOCs, yielding a cycle time of approximately 10 minutes. Intercomparisons between the PTR-MS's and other VOC measurements conducted on Appledore Island and Thompson Farm during the summer campaign are in good agreement overall. Other measurements that were deployed on the island included mist chamber/ion chromatography measurements for acetic acid, canister samples analyzed by GC-ECD/FID/MS and an in situ, cryo-less GC system for NMHCs and OVOCs. Trace gas distributions will be presented in addition to the local and regional impact on ozone production in New England from reactive VOC enhancements.
A53C-0921 1340h
Long-range urban plume transport during the ICARTT campaign: an analysis of Lagrangian balloon observations
During the summer of 2004, five satellite-controlled airmass tracking balloons, developed at the University of Massachusetts, were flown as part of the International Consortium for Atmospheric Research on Transport and Transformations (ICARTT) campaign. These balloons are notable for their small size (~1 kg mass), unique altitude-control, and long-duration flight capability. The balloons were embedded in urban plumes from New York and Boston which they tracked over New England, Eastern Canada and the Atlantic Ocean. Flights ranged from 12 to 120 hours in duration and covered a maximum distance of 3000 km. The balloons helped guide Lagrangian and semi-Lagrangian aircraft observations of ozone, precursor molecules, and aerosols. Balloon-based meteorological and, in one flight, ozone observations are analyzed in the context of model trajectories, as well as aircraft, satellite, and ground station data. The accuracy of the balloons as Lagrangian tracers is accessed, providing the basis for an improved understanding of regional air pollution.
http://www.rparl.org